Hematopoietic stem cell (HSC) numbers are carefully maintained by switching from symmetric to asymmetric cell divisions. A complex program made of genetic and epigenetic mechanisms that maintain normal HSCs can become dysregulated in hematopoietic disorders and malignancies. Myelodysplastic syndromes (MDS) are characterized as a clonally derived set of heterogeneous diseases demonstrating defective hematopoietic differentiation. Taken together with recent discoveries in the genetic landscape of MDS, the etiology of this disease is considered to be driven by an HSC or an early myeloid progenitor. Thus, dysregulation of cell fate decisions including the balance of asymmetric and symmetric cell division could explain how certain lineages are blocked or why self-renewal is altered. RNA binding proteins in the Msi family have been shown to be important for the switch between symmetric and asymmetric cell division in germ and tissue stem cell function, neural cell differentiation and cell fate determination. Recent studies have implicated MSI2 as a regulator of HSC function and this proposal utilizes Msi2 conditional knockouts and gain of function approaches to dissect the precise role for MSI2 in controlling asymmetric division, self-renewal and cell fate determination. Moreover, this proposal incorporates high throughput sequencing UV-crosslinking immunoprecipitation to identify global RNA targets (HITS-CLIP) that will be used to elucidate the direct mechanism for MSI2 in hematopoietic cells. Furthermore, our global genetic approaches have already uncovered how regulation of translation alters several developmental pathways. MSI2 has also been recently shown to be dysregulated in MDS within low- risk patients, expressing below normal levels and within high-risk patients demonstrating elevated MSI2 expression. This proposal utilizes the NUP98-HOXD13 MDS murine model combined with novel gain and loss of function MSI2 mouse models to study the initial stages of MDS within the HSC. We suggest that MSI2 dysregulation contributes to the biology of hematopoietic disorders and thus a deeper understanding of these mechanisms will provide additional therapeutic approaches.